Simple variable assignment triggers out of bonds exception in Visual Studio Code

Learning
1

Here is a precise list of all the actions I did :

  1. Write let a=7;; (exactly this line and nothing else) in file debugger.ml
  2. In my terminal, do ocamlc -bin-annot -g -o debugger.d.cmo -c debugger.ml
    followed by ocamlc -bin-annot -g -o debugger.ocaml_debuggable debugger.d.cmo
  3. In debugger settings, set the “program” line to
    “program”: “${workspaceRoot}/debugger.ocaml_debuggable”
  4. Set a breakpoint on the unique line in debugger.ml
  5. Click “Start debugger” in main menu.

And I get the following error message :

Can anyone explain why this happened and how to fix it ?